We shall explore some aspects of the genetic homology between the Major Hisotocompatibility Systems of mice and humans. We shall study the linkage of murine Bf (factor B of properdin), PGM-3 (phosphoglucomutase-3), GLO (Glyoxalase-1) and C-3 (third component of complement) to the H-2 locus (the murine MHS), and determine their linear order and relative distances. This will be done by adequate crosses between mice heterozygous for these loci, derived from the non-inbred Swiss-Webster strain and inbred animals, using the double-, and when possible, the triple-backcross situation. We also plan to study the homology between the blood groups Chido in humans and H-2.7 in mice, the loci of both of which map within their respective MHS. This study will be done by determining serological cross reactivities and immunochemical associations particularly with beta-2m (beta-2 microglobulin). The relation between C 2-deficiency and the HLA system will also be studied by screening a large number of normal blood donors for absence of hemolytic complement activity. We expect to ascertain from these studies the degree to which the structure of the MHS as a linkage group (i.e., sequence and relative distance of the loci involved) has remained constant throughout evolution. We anticipate that this research will lead to the proposal of experimental approaches to elucidate the nature of the associations between the products of these loci that underlies the stability of their linkage.